Control apparatus



INVENTOR. Gia/resfrfN/rms TRNY I G. F. JENKINS CONTROL APPARATUS "Filedoct. 19'45 Nov. 8, 1949 Patented Nov. 8, 1949 2,487,556 CONTROLAPPARATUS George F. Jenkins, Minneapolis, Minn., assignor toMinneapolis-Honeywell Regulator Company, Minneapolis, Minn., acorporation of Delaware ApplicationOctober 8, 1945, Serial No. 620,983

Claims.

The present invention comprises heat control apparatus whereina rise intemperature of a space being heated is anticipated by a selfgeneratedincreased temperature of the temperature sensing element. l

It is a common characteristic of heat control systems to ignore the heatcapacity of the heating means used. As a consequence, after the heatingmeans has been stopped or deenergized by the temperature responsivemeans in the space being heated, the temperature in said space continuesto rise due to the dissipation of the residual heat of the heatingmeans. In addition to the heat capacity of the heating means tending tocause overrunning of the desired temperature, the time lag of thetemperature responsive element in responding to the averagetemperatureof the space being considered also tends to cause the spacetemperature to exceed the desired value.

It is therefore an object of the present invention to provide improvedtemperature control apparatus capable of anticipating a change intemperature due to the energizing of the temperature changing means.

It is a further object to provide an improved temperature control systemusing a temperature responsive resistor sensing element wherein a risein temperature is anticipated by increasing thetemperature of saidresistor.

It is an additional object to provide temperature control. apparatus ofthe resistance bridge type wherein the Voltage imposed on said bridge isvaried in response to the energizing of temperature changing means.

It is also an object to provide temperature control apparatus in whichthe ambient temperature of the apparatus, excluding the temperatureresponsive element, is of little consequence.

It is another obj ect to provide temperature control apparatus of theresistance bridge type and capable of temperature change anticipationwhich is simple and dependable and involves a minimum of wiring andequipment.

It is a further object to provide heat control apparatus of a precisiontype including the feature of heat anticipation to further increase theaccuracy of the apparatus.

It is an additional object to provide heat control apparatus of theresistance bridge sort wherein heat anticipation is provided byincreasing the It is also an object to provide a temperature.

control system usable with either heating or cooling equipment andcapable of anticipating changes in temperature in either direction withonly minor modifications.

These and other objects will become apparent as the descriptionproceeds.

The single figure of the drawing shows l schematically the presentapparatus and the connections thereof.

In the drawing, an enclosed space I0 is heated by an electric heatingelement II, the electric heating element being illustrative of anyheating means that can be electrically'controlled. The enclosed space I0may be an oven, a room or other enclosure, or may be consideredrepresentative of a medium the temperature of which it is desired tocontrol.

A temperature sensing element I2 comprises a vresistor having arelatively high temperature coeilicient of resistance and forms part ofa bridge or voltage dividing network circuit generally designated by thenumeral I3. As shown, wire I4, resistor I2 and wire I5 forms the lowerright hand branch of the bridge; resistor I6 yand adjustable wiper I9forms the lower left hand branch; resistor I1, the upper left handbranch; and resistor I8 forms the.upper right hand branch of the networkcircuit. Connections 20 and 2| form the input terminals and connections22 and 23 form the output terminals of network I3. Resistor I2 is4preferably made of material having a relatively high temperaturecoefficient of resistance such as nickel, whereas resistors I6, I1 andI8. are preferably made cf material having a relatively low temperaturecoeflicient of resistance, such as manganin. The balance of the network,orthe control point, may be adjusted by varying the position of wiper I9on resistor I6.

A transformer 25 having a primary winding 26 and a's'econdary winding 21provides a source of electric current for energizing the network circuitI3. Secondary winding 21 includes a terminal 28, an intermediate tap 29and a terminal 30. Primary winding 26 is connected to line wires 3| and32 by wires 33 and 34, respectively.

An amplifier 40 is connected to output terminals 22 and 23 of network I3by wires 42 and 43, respectively, and actuates a relay in response tothe conditions of balance of said network. Ampliiler 40 may be of anysuitable sort but preferably is of an electronic null point type.However, it is noted that amplifying means comprising a sensitive relay,such as one of the depressor bar type, is entirely adequate for manyinstallations.

Relay 45 is conventional and includes a winding 46, a switchr blade 41engageable with in concasacca tact 46, and a switch blade it engageablewith in contact t@ or out contact i.

To better illustrate the coaction oi the above apparatus. attention isdirected to the ifollowing description of operation.

Operation With the present apparatus in the position shown. it may beconsidered that the temperature requirements in the enclosed space lllare satisfied, bridge network i3 is balanced, relay 45 is deenergizedand no current is being provided heating element Il. The desiredtemperature to be maintained has been selected by adjusting wiper I9 onresistor I5 to a point wherein the bridge will be balanced when resistorI2 is at the selected temperature. Bridge I3 is energized by apredetermined voltage, volts for instance, by the circuit: tap 25 oftransformer secondary winding 2l, wire 55, out contact 5I and switchblade I9 of relay I5, Wire 55, terminal 2B of network It, terminal 2l ofsaid network, wire 5l, and terminal 28 of said secondary winding.Ampliner 4d is supplied current by the circuit: line wire 3i, wire 4I,amplier BIB, wire d2, and 'line wire 32.

If the temperature in space III should now decrease, the temperature ofresistor I2 will fall accordingly. A decreased temperature of resistorI2 results in a lowered resistance of same and thereby causes anincreased current flow in the right hand side of the bridge network.This causes a potential difference to exist between output terminals 22and 23 of the network, thereby providing a signal voltage to amplifiertILthe connections being previously described. The signal potential inthe input of amplifier Ill) causes operation thereof resulting in theenergizing of relay 65 by the circuit: an output terminal of ampliiierH0, wire 56, relay winding 4S, wire 59 and the other output terminal ofsaid amplifier.

Energizing relay 45 causes the same to pull in its switch blades andthereby energizcs heating element II by the circuit: line wire 3|, wire6I, contact t8 and switch blade 4l of relay 45, wire 62, heating elementII, wire 53, and line wire 32. At the same time, switch blade i9 ispulled out of engagement with contact 5I and into engagement withcontact 5d.

Network I 3 is now energized by the circuit: terminal 30 of secondarywinding 2l, wire 64, contact 50 and switch blade t9 of relay 45, wire56, terminal 20 of network i3, terminal 2i of the same, wire 51, andterminal |28 of winding 21. This causes the maximum voltage availablefrom transformer 25, such as 20 volts, to be imposed 4on the networkcircuit.

With heating element Il energized and war ing space I0, the temperatureof the same rises, thus tending to cause the temperature of resistor I2to rise accordingly. However, since the network now has twice theprevious voltage imposed on it, substantially twice the current is owingthrough the branches of the network. This re= sults in four times asmuch heat in the resistors due to current ilow as previously and therebyraises their temperatures. 'Ihe increase in tem perature of resistorsI6, Il, and I8 is of little or no consequence because of their lowtemperature coeicients of resistance, but due to the relatively highcoeiilcient of resistance of resistor I2, its resistance is increasedsumciently to simulate a few degrees temperature increase in space I0.Thus the temperature of space Ill is increased by heating element I Iand simultaneously therewith,

the operating temperature of resistor I2 is increased to a valuepreferably a few degrees above the space temperature. The actualtemperature to which resistor I2 responds, at any moment while heater ilis energized, may thus be considered to anticipate a rise in thetemperature of space Ib.

When the operating temperature of resistor I2, due to its own heat andthe temperature of space I0, rises suiilciently high, and therebyincreases its resistance suiciently izo-balance network I3, an inputsignal voltage is no longer furnished ampliner 46 and relay 45 istherefore deenergized. With relay d5 deenergized, switch blade Il dropsout of engagement with contact 48 and heating element II is deenergized.Further, switch blade Q9 again engages contact 5l instead of 50 therebyreducing the voltage on network i3 and reducing the heating of saidresistors due to current ilow to a negligible value. At the moment relay45 is deenergized, the actual temperature in space It may be, forinstance, 2 or 3 degrees below that desired, resistor l2 being at thedesired temperature due to its added heat. Now, when the voltage on thenetwork is reduced and the added heat in resistor I2 is dissipated tospace IB, thus tending to lower its temperature, it should be noted thatthe residual heat of resistor II is also being dissipated to space I0.This raises the temperature in space III a few degrees even though thecurrent supply to the heater has been cut off. The net result is thatthe temperature of space l0 levels oi at the desired value, overshootingof the temperature being prevented by anticipating the rise intemperature due to residual heat of the heating means. In addition, asthe rate of heat transfer from the heating means II is gradually loweredas the said means loses its heat, the resulting lower rate oftemperature change in the space I0 permits resistor I2 to moreaccurately respond to the average temperature of the space by reducingthe effect of lag.

The present apparatus may also be used for control of cooling apparatusby substituting cooling means for heating means I I and by connectingtap '29 to contact 50 and terminal 30 to contact 5I. The inputconnections to amplier 40 may also need to be reversed, depending uponthe particular amplier used. With these changes, resistor I2 wouldnormally be heated a few degrees above the space temperature due to thefull voltage imposed on the network. However, when the space temperaturerises suiliciently to unbalance the network and cause the ampli- :fier40 to energize relay 45, thus causing operation of the cooling means,the reduced voltage then imposed on network I3 would reduce the heatingof resistor I2 and thus anticipate a reduction in space temperature.

While the present invention has been illustrated and described in itspreferred form, many alternatives and substitutions will be readilyapparent to those skilled in the art. The present disclosure shouldtherefore be considered as illustrative only, with the scope of theinvention being determined solely by the appended claims.

I claim:

1. In a temperature control system, in combination, means for heating amedium, a bridge network circuit having input and output terminals andincluding a resistor having a relatively high temperature coeilicient ofresistance responsive to the temperature of said medium, amplifiermeans, means connecting the output terminals of said network to saidamplier means, relay means including switch means for controlling saidheating means and additional switch means, a transformer including asecondary winding for supplying an electric current to the inputterminals of said network circuit, said secondary winding havingterminals and an intermediate tap, and means including said additionalswitch means for connecting said secondary winding to the inputterminals of said network in such manner that said additional switchmeans determines whether said tap or a terminal of said secondarywinding is connected to one of the input terminals of said network.

2. In a temperature control system, in combination, controllable meansfor changing the temperature of a medium, a voltage dividing networkincluding a resistor having a relatively high temperature coefficient ofresistance responsive to the temperature of said medium, amplifiermeans, circuit means connecting the output of said network to saidamplifier, means adapted to be connected to a source of electricity forimposing a predetermined voltage on the input of said network, switchingmeans controlled by said ampliiier for causing operation of saidtemperature changing means when the medium temperature varies to apredetermined Value, and circuit means also controlled by said amplifiermeans to cause a'substantially different voltage to be imposed on saidnetwork when said temperature changing means is caused to operate.

3. In a heat control apparatus, means for heating a medium, means forcontrolling said heating means, temperature responsive resistor meanshaving a relatively high temperature coeicient of resistance forresponding to the temf perature of said medium, amplifier means,normally balanced electric network circuit means including' saidresistor for controlling said amplifier means, supply means for causinga relatively small electric current to flow in said network circuit, andswitching means controlled by said amplier means for actuating saidcontrol- 'ling means and simultaneously increasing the current flow insaid circuit so that the current flowing through said resistor willincrease the temperature of the said resistor and thereby increase itsresistance.

heating means, resistor means having a relatively high temperaturecoeicient of resistance for responding to the temperature of saidmedium, ampliiier means, electric circuit means including said resistorfor controlling said amplifier means, circuit means including a pluralvoltage transformer for imposing a predetermined potential on saidcircuit means, and switching means controlled by said ampliiier meansfor causing operation of said heating means and for considerablyincreasing the potential imposed on said circuit means by saidtransformer.

5. In a control apparatus for a heating system, temperature sensingmeans comprising a network circuit including a resistor having arelatively high coefiicient of resistance, electrical means for Variablyenergizing said network circuit, amplier means controlled by saidnetwork circuit for controlling said heating system, and switching meansoperated by said amplifier means for anticipating a rise in temperatureat said sensing means by varying the energizing current in said networkcircuit and resistor.

GEORGE F. JENKINS.

REFERENCES CITED 4 The following references are of record in the file ofthis patent:

